Which of the following conferencing features requires a Cisco VCS and a Cisco MCU?

A.
only MultiSite

B.
only Multiway

C.
both MultiSite and Multiway

D.
neither MultiSite nor Multiway

Explanation:
Only Multiway requires a Cisco TelePresence Video Communication Server (VCS) and a Cisco TelePresence
multipoint control unit (MCU). MultiSite and Multiway provide ad-hoc, or on-demand, conferencing.
MultiSite uses a phone’s native MCU functionality, so it does not require a Cisco MCU or a Cisco VCS.
However, it requires that a MultiSite option key be installed on each endpoint. By contrast, Multiway uses
dedicated external conferencing resources but does not require an option key on the endpoints. MultiSite and
Multiway are mutually exclusive; if Multiway is used on your network, you should disable MultiSite on the
endpoints.
MultiSite allows four simultaneous participants on a video call. Multiway allows many more participants and is
limited only by the MCU that controls the conferencing. To participate in an ad-hoc conference, simply press the
Conf, Join, cBarge, or Add keys on the endpoint.

Cisco: Using Multiway with Cisco TelePresence systems
Cisco: Cisco Rich Media Conferencing: Ad-hoc Audio Conference
Cisco: Cisco TelePresence SX20 Quick Set, Product Overview (PDF)